1. A method of attaching a toner cartridge to a developing unit, the toner cartridge includinga housing accommodating toner therein and having a first opening allowing toner to be discharged therefrom, an auger rotatable about a first axis extending in a first direction and configured to convey the toner to the first opening in the first direction, the auger having one end portion and another end portion positioned apart from the one end portion in the first direction, a first protrusion extending in the first direction and being positioned closer to the one end portion of the auger than the another end portion of the auger is to the one end portion of the auger, the first protrusion being rotatable relative to the housing, and a second protrusion extending in the first direction and being positioned closer to the another end portion of the auger than the one end portion of the auger is to the another end portion of the auger, the method comprising:inserting the first protrusion into a corresponding first groove of the developing unit;inserting the second protrusion into a corresponding second groove of the developing unit; andin a state where the first protrusion is received in the first groove and the second protrusion is received in the second groove, pivoting the housing of the toner cartridge relative to the developing unit.